Means in furnaces for vacuum-pressure-sintering

ABSTRACT

A furnace for vacuum-pressure-sintering has a furnace chamber which is enclosed in and insulated from a surrounding pressure chamber. The pressure chamber includes a bottom projecting into it at the lower end and has at the upper end a charging opening and a lid projecting into the charging opening. A housing can be applied over the charging opening and connected to a vacuum pump during the part of the operating cycle when the pressure in the furnace is to be below atmospheric pressure. The lid is formed of an outer annular part and an inner part, separate from each other, the outer annular part remaining in position when the inner part is removed. A heat radiation protection ring is provided for insertion into the opening into the annular part when the annular part is raised. A lifting device for the lid is provided inside the housing.

United States Patent [191 Johansson et al.

[4 1 Nov. 27, 1973 MEANS IN FURNACES FOR VACUUM-PRESSURE-SINTERING [75Inventors: Paul Johansson; Torstein Landa, 7

both of Vasteras; Hans Larker, Robertsfors, all of Sweden [73] Assignee:Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden Mar. 13, 1972[21] Appl. No.: 233,925

[30] Foreign Application Priority Data Mar. 15, 1971 Sweden 3276/71 [52]US. Cl. 432/205, 13/31 [51] Int. Cl. F271) 3/18 [58] Field of Search263/40; 13/31; 432/205 '[56] References Cited UNITED STATES PATENTS3,427,011 2/1969 Boyer et al.... 263/40 R 3,243,174 3/1966 Sweet 13/31 X3,522,357 7/1970 Pine et al 13/31 9/1967 Westeren 263/40 R PrimaryExaminer-John J. Camby Attorney.lennings Bailey, Jr.

57 ABSTRACT A furnace for vacuum-pressure-sintering has a furnacechamber which is enclosed in and insulated from a surrounding pressureChamber. The pressure chamber includes a bottom projecting into it atthe lower end and has at the upper end a charging opening and a lidprojecting into the charging opening. A housing can be applied over thecharging opening and connected to a vacuum pump during the part of theoperating cycle when the pressure in the furnace is to be belowatmospheric pressure.

The lid is formed of an outer annular part and an inner part, separatefrom each other, the outer annular part remaining in position when theinner part is removed. A heat radiation protection ring is provided forinsertion into the opening into the annular part when the annular partis raised. A lifting device for the lid is provided inside the housing.

15 Claims, 5 Drawing Figures sum 2 BF 3 PATENIEDnuv 21 I975 Fig. 2

///H////////M/// /////Z MEANS IN FURNACES FOR VACUUM-PRESSURE-SINTERINGBACKGROUND or THE INVENTION 1. Field of the Invention The presentinvention relates to an arrangement for .use with a furnace forvacuum-pressure-sintering having a furnace chamber which is enclosed inand insulated from a surrounding pressure chamber composed of a pressurecylinder, a bottom projecting into this cylinder and a lid projectinginto the charging opening of the furnace. t

2. The Prior Art 1 High density and freedom from pores gives highquality cemented carbide bodies produced metallurfgically from powder.In chip cutting machines the high density results in increased water andless risk of broken cutting edges. For rollers and the like the freedomfrom pores results in increased strength and surface smoothness and thisalso results in a smoother surface for a product being rolled. Even inthe production of electrical resistance bodies of Mosi for example,there are considerable advantages in having a very high density andfreedom from pores. The strength increases and the risk of localover-heating with resultant burning decreases. The advantagesofhighdensity and freedom from pores are equally great forcermets ofvarious types. i v I High density and freedom from pores have previouslybeen obtained (See, for example, Materialsin Design Engineering May1965, pages 92-99), by enclosing a compacted powder body in a gas-tight,heat-resistant casing of some suitable metal, then evacuating thecasing, sealing it and placing it in a furnace in which the material issintered under high pressure. Temperatures and pressures of up to 1,500Cand 2000 bars have been used. It is extremely expensive to apply acasing around a pressed body, particularly if it has a complicatedshape, to evacuate and seal the casing and finally to remove the casingafter the sintering. Especially in the production of small cuttingelements the encapsuling is disproportionatelyexpensive. The problem hasbeen how to make it possible to perform sintering and hot-moulding undersuch" conditions that the desired quality is obtained without expensiveencapsuling.

I A method is known (See French pat. no.'2,036,654) for manufacturingsintered powder bodies having high density which comprises sintering,preferably under vacuum, powder bodies which have been moulded in theconventional manner by compressing powder and then hot-moulding thebodies after the sintering under direct influence of a pressure medium.The sintering of the bodies and the subsequent compression are thuscarried out without the bodies being enclosed in a gastight casing.According to this method, bodies manufactured from a powder'or powdermixture are sintered at atmospheric pressure or lower pressure and atsuch a temperature that powder particles of the same material are boundtogether-or that binder binds together other powder particles in thepowder mixture, after which the bodies are isostatically hot-moulded inthe same furnace under direct influence of a pressure medium such asargon, helium, nitrogen or hydrogen. One possible explanation for thedensity increasing due to isostatic hot-moulding of sintered productsalthough the bodies are not enclosed in special casing which prevent thepressure medium from coming into direct contact with the body may bethat spaces'formed between powder particles bound together arecompletely sealed.

The binder thus forms a closed capsule around each individual space andprevents the pressure medium from penetrating into the body. During thesubsequent hot-' moulding, these cavities disappear in the same way asthey do when the hot-moulding is carried out with the material enclosedin a casing when pressure and temperature are chosen so that the binderis sufficiently easily deformed so that powder'particles bound to getherwill slide towards each other and fill out the empty cavities.

To illustrate the technical progress brought about by the method of theFrench patent, it may be mentioned that sintered bodies which aremanufactured according to. conventional methods usually contain 100 500times as many cavities per unit of volume as bodies manufactured inaccordance with that method. In comparison with previous methodscomprising pressuresintering powder bodies enclosed in an evacuatedheatresistant casing, the advantage is gained that a timeconsuming andexpensive stage in the production is eliminated. The process makespossible sintering without encasing, without cooling of the bodiesbetween sintering and hot-moulding and without complicated transfermeans with sluices to prevent hot bodies from coming into contact withair. When compacting uranium dioxide, U0 a density ofup to 99.5 percentof the theoretically achievable density can be obtained.

There is a fumace for this method (See French Pat. No. 2,021,436) inwhich both sintering, and hotmoulding can be performed and which istherefore especially suitable for carrying out the method.The furnace isof the type comprising a cylindrical pressure chamber with a highpressure cylinder, end closures projecting into this cylinder, and meansto take up axial forces exerted on the end closures by a pressure'medium enclosed in the pressure chamber. The furnace chamber andheating means of the furnace are surrounded by an insulating casing inthe shape of a sleeve with insulating lid and bottom. I I

Moulding is performed immediately after the sintering and is started atthe sintering temperature. During the moulding the temperature must besetat at least such a value that the binder can be deformed enough toallow the sealed spaces to be compressed. Temperature and pressure aredependent upon eachother and on the powder composition.

SUMMARY OF THE INVENTION:

- during the part of the operating cycle when the pres sure in thefurnace is to be below atmospheric pressure.

The lid is formed of an outer annular part and an inner part, separatefrom each other, the outer annular part remaining in position when theinner part is removed. A heat radiation protection ring is provided forinsertion into the opening into the annular part when the annular partisraised'. A lifting device for the lid is provided inside the housing.

By the introduction of a device according to the invention into thefurnace, the risks of oxygen or air penet'ration which otherwise existin such furnaces are completely eliminated and the lower side of thecharging opening lid' can thus also be protected the whole inventionincludes a lid 14 to close the charging open time and by means of saidprotective collar and radiation protection means the sealing surfaces ofthe charging opening are effectively protected and, which is extremelyimportant, the degassing time decreases which 7 is of great importancefor the length of the process. Previously said furnaces have been usedwith a central hole for degassing. It is then desirable for this hole tobe as large as possible in order to decrease the degassing time, butbecause of the strength required during the pressure cycle the size ofthe hole must be limited and there are also considerable problems withinsulation.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERREDEMBODIMENTS In the drawings 1 designates a press stand which is movablebetween the position shown in the drawing and a position where itsurrounds the high pressure chamber 2. The press stand is of the typecomprising yokes 3 and 4, spacers 5between the yokes and a strip mantle6. The stand is carried by wheels 7 running on tracks 8. The highpressure chamber 2 is carried by a pillar 9. This comprises a highpressure cylinder consisting of an inner tube 10 and a surrounding stripmantle 11 with end rings 12 holding the strip mantle together axiallyand providing attachments for brackets .13 by means of which the highpressure chamber 2 is attached to the pillar 9. The chamber 2 has anupper end closure 14 which projects into the tube 10 of the highpressure cylinder through a pipe flange 15 attached to the tube andprovided with sealing surfaces.

The pressure chamber 2 has a lower end closure which consists of anannular outer part 19 attached and projecting beneath the tube 10 and alid 20 projecting into the tube. A ring 21 rests on the part 20 of theend closure. This is fixed to the part 20 in a manner not shown andsupports the insulating casing 24 which surrounds the furnace chamber 22where a billet-23 is being treated, the billet being supported by aninsulating bottom joined to the lid 20. Inside the insulating casing 24which surrounds the furnace chamber 22 are electrical heating elements31 which are passed through conduits 32 connected to lead-ins in theannular part 19 of the end closure.

ing. The lid is suitably constructed in sections with decreasing radii,the section having the greatest radius resting on said pipe flange 15when the lid l4-is placed over the opening. The lowermost section of thelid 14 suitably consists of an'insulating material. Channels 17 forcoolant are provided in the lid.

The lid 14 is connected by an arm 18 to a lifting device 36 which isarranged to raise and lower said lid to highest and lowest positions,respectively. Channels 37 for coolant run through this arm 18 and thedevice 36. Both positions of the lid are shown sectioned in FIG. 1. Inits lowest position (see the lefthand section) the lid 14 completelycloses the charging opening 25. In its uppermost position the lid 14 isnot in contact with the pressure chamber, but a gap 25 is formed betweenthe lid 14 and the charging opening.

According to the invention a housing 26 is positioned above the chargingopening 25 and the lid 14. The housing 26 is provided with an annularbottom flange 33 which rests against a base flange 34 on the pressurechamber 2. A sealing ring 35 is placed along the entire contact surfacebetween the flanges. A vacuum pump equipment, notshown, is connected bya valved connection 28 to the housing 26, which can be lifted by meansof the external lifting members 27. Cooling channels 29 are provided inthe walls of the housing 26.

According to the invention there is a radiation pro.- tection means 40between the charging opening 25 and the furnace chamber 22 and above thelatter, (See FIG. 2). The radiation protection means 40 is divided intoa lower annular radiation plate section 401 which, through theinsulating support 404, rests directly-on the furnace chamber 22 andinto an upper circular radia tion plate section 402 which is anchored tothe lower section 401 and is held in place at a specific distance fromthe lower section by spacer elements 405. Lifting yokes 403 may beconnected to the spacer elements 405 on the upper side of the uppersection 402, which are used when the radiation protection means must beremoved while charging the furnace. The radiation plate sections 401 and402 preferably consist of composite molybdenum plates. A channel 406,indicated with an arrow in the drawing, shows the path travelled by thegases during the vacuum cycle. It is important that the gas always flowsthrough the same throughflow area so that the gas flow is not throttledand because of this the degassing time is considerably reduced.

According to the invention there is also a protective collar 50, shownin FIG. 3, this figure also showing an alternative embodiment of thepipe flange 15. The protective flange 50 is preferably positioned in thecharging opening during the vacuum cycle of the furnace when the lid 14is not closed, to prevent the sealing surfaces of the pipe flange 15from being subjected to heat radiation and impurities. The protectiveflange 50 is suitably provided with heat radiation protective material.By means of a member 60 or connected in the wall or roof of the housing26 in accordance with FIG. 4 or 5 said protective collar 50 can easilybe applied and removed. The member 60 according to FIG. 4 starts withthe collar in position 501. The collar is projected into the housing 26to position 502 with the help of a toothed rack 61, after which it islowered into position 503, for example by means of a trolley runningmeans of a perpendicularly applied toothed rack 71 enclosed in acontainer 72 fitted to the housing 26. The toothed rack 71 is driven bymeans of a shaft 73 connected to a driving means 74 fixed by means of astay 75 to the housing 26. FIG. also'shows an alternative 14 is loweredto its lowermost position and when the embodiment of the housing 26.

As described above, the process in said furnace takes place in twophases, a vacuum cycle and a pressure cycle.

During the vacuum cycle the charge is degassed and the lid 14 is then inits highest position and the housing 26 is positioned over the chargingopening and' the lid, as shown in the righthand part of FIG. 1. Duringthis cycle it is possible, as seen previously, to placea protectiveflange 50 in the charging opening as shown in FIGS. 3, 4 and 5..Theradiation protection means 40 is in position according to FIG. 2immediately after charging has taken place and before the furnaceprocessing starts.

comprising an inner circular part and an outer annular part, the outerpart remaining in the charging opening when the central part of the lidis lifted.

' 3. In a combination according to claim 1, the lower part of the lidconsisting of insulating material,

4. In a combination accordingto claim 1, said lifting means beingarranged on said housing.

5. In a combination according to claim I, cooling channels in the wallsof said housing.

- When the vacuum cycle is complete,-the protective ring 50 is removedby a member 60 or 70 and the lid charging opening has been closed thehousing 26 can be removed by an external lifting device with the help oflifting members 27. The stand 1 is moved in over the furnace chamber 2and the pressure cycle can start.

The invention is of course not limited to the embodiment shown anddescribed. Many variations are feasible within the scope of thefollowing claims.

We claim:

1. In combination with a furance for vaccum-pressure-sintering having afurnace chamber which is enclosed in and insulated from a surroundingpressure chamber composed of a pressure cylinder, a bottom projectinginto said pressure chamber, a lid projecting into the charging openingof said furnace, the improvement comprising means for raising andlowering saidlid between upper and lower positions, and a housing whichcan-be applied over said charging opening and Eonnected to a vacuum pumpduring that part of the operating cyclewhenv the pressure in saidfurnace is below atmospheric pressure, said lid being enclosed by saidhousing in said furnace and forming a gap between said lid and saidcharging opening during the vacuum cycle, and said lid closing saidcharging opening when said housing is removed fromit.

2. In a combination according to claim 1, said lid 6. In a combinationaccording to claim 1, the furnace around the charging opening beingprovided with a base flange fixed to the furnace said housing having aconnecting flange applicable against said base flange.

7. In a combination according to claim 6, one of said flanges having aseal running along the entire contact surface.

8. In a combination according to claim 1, a heat radiation protectionmeans arranged above the furnace chamber. I

' 9. In a combination according to claim 8, said radiation protectionmeans comprising radiation plate sections.

10. In a combination according to claim 9, the radiation protectionmeans comprising a lower and an upper section of radiation plates, thelower section being annular, support members at the upper part of saidfurnace chamber, said lower section resting on the support members, theupper section being circular and having a radius greater than the innerradius of said lower section, and a spacer element fixing the uppersection at a distance from the lower section.

1 1. In a combination according to claim 10, the area of theopening ofthe lower radiation plate section, the

area of the gap between the radiation plate sections and the areabetween the upper radiation plate section and the surrounding wall beingsubstantially equal.

12. In a combination according to claim 10, a gripping means for theupper radiation plate section on its upper side to permit lifting of theentire radiation protection means. 7

13. In a combination according to claim 9, said radiation plate sectionscomprising molybdenum plates.

14. In a combination according to claim 1, an annular protective collarmounted to be lowered into said charging opening and arranged to protectthe area of the opening when in lowered position.

15. In a combination according to claim 14, operating devices insidesaid housing for positioning said protection collar in said opening.

1. In combination with a furance for vaccum-pressure-sintering having afurnace chamber which is enclosed in and insulated from a surroundingpressure chamber composed of a pressure cylinder, a bottom projectinginto said pressure chamber, a lid projecting into the charging openingof said furnace, the improvement comprising means for raising andlowering said lid between upper and lower positions, and a housing whichcan be applied over said charging opening and connected to a vacuum pumpduring that part of the operating cycle when the pressure in saidfurnace is below atmospheric pressure, said lid being enclosed by saidhousing in said furnace and forming a gap between said lid and saidcharging opening during the vacuum cycle, and said lid closing saidcharging opening when said housing is removed from it.
 2. In acombination according to claim 1, said lid comprising an inner circularpart and an outer annular part, the outer part remaining in the chargingopening when the central part of the lid is lifted.
 3. In a combinationaccording to claim 1, the lower part of the lid consisting of insulatingmaterial.
 4. In a combination according to claim 1, said lifting meansbeing arranged on said housing.
 5. In a combination according to claim1, cooling channels in the walls of said housing.
 6. In a combinationaccording to claim 1, the furnace around the charging opening beingprovided with a base flange fixed to the furnace said housing having aconnecting flange applicable against said base flange.
 7. In acombination according to claim 6, one of said flanges having a sealrunning along the entire contact surface.
 8. In a combination accordingto claim 1, a heat radiation protection means arranged above the furnacechamber.
 9. In a combination according to claim 8, said radiationprotection means comprising radiation plate sections.
 10. In acombination according to claim 9, the radiation protection meanscomprising a lower and an upper section of radiation plates, the lowersection being annular, support members at the upper part of said furnacechamber, said lower section resting on the support members, the uppersection being circular and having a radius greater than the inner radiusof said lower section, and a spacer element fixing the upper section ata distance from the lower section.
 11. In a combination according toclaim 10, the area of the opening of the lower radiation plate section,the area of the gap between the radiation plate sections and the areabetween the upper radiation plate section and the surrounding wall beingsubstantially equal.
 12. In a combination according to claim 10, agripping means for the upper radiation plate section on its upper sideto permit lifting of the entire radiation protection means.
 13. In acombination according to claim 9, said radiation plate sectionscomprising molybdenum plates.
 14. In a combination according to claim 1,an annular protective collar mounted to be lowered into said chargingopening and arranged to protect the area of the opening when in loweredposition.
 15. In a combination according to claim 14, operating devicesinside said housing for positioning said protection collar in saidopening.